Electrolytic apparatus



3 Sheets-Sheet l INVENTOR azz-m .'A TTORNEY aange Dec. 5, 1933. G, BAUMELECTROLYTIC APPARATUS Original Filed Jan. 3. 1927 1 wwwmw.

i Dec. 5, 1933. G BAUM 1,937,621

ELECTROLYTIC APPARATUS original Fi1ed Jan. 5, 1927. 3 sheets-sheet '2ATTORNEY Dec. 5, 1933. G. BAU

ELEGTROLYTIC APPARATUS Original Filed Jan. 3, 1927 3 Sheets-Sheet 3 ATTORN EY Patented Dec. 5, 1933 UNITED STATES PATENT OFFICE ELECTROLYTICAPPARATUS Gustav Baum, Weissenstein above the Drau, Austria., assignor,by mesne assignments, to E. I. du Pont de Nemours and Company, acorporation of Delaware Original application January 3, 1927, Serial No.158,457, now Patent No. 1,837,177, and in Austria January 28, 1926.

Divided and this application May 8, 1931. Serial No. 535,819

12 Claims. (Cl. 204-9) Persulphuric acid or the persulphates can bedecomposed or hydrolyzed to give sulphuric acid, or sulphates, as thecase may be, and hydrogen peroxide.

It has heretofore been proposed to electrolyze an aqueous solution ofsulphuric acid in a cell having a platinum anode in the anolyte, and alead cathode in the catholyte, the anolyte and the catholyte beingseparated by a porous diaphragm. Such arrangements have not heretoforeto my knowledge been commercially successful for a number of reasons.Among these are excessive heat generated in the cell by internalresistance, decomposition of product and side reactions due to the heatgenerated, low current density, contamination of anolyte due toprolongation of the time of. electrolysis in the effort to increase theyield, polarization of the anode, etc. It has been attempted to overcomethe objection of heating by cooling the anode and the electrolyte, butthese expedients have only been of slight benefit to the yield or to theefficiency and have not reduced the expense of installation and ofmaintenance to such extent as to be of practical benefit.

I have discovered that a minimum internal resistance of a diaphragm cellof this type is not only necessary to reduce heating but is also ofdecided advantage in permitting higher current concentrations to beused, and that the higher the current concentration used, the greaterthe unit conversion to persulphuric acid. I have furyther found that inorder to avoid side reactions or decomposition in a cell having highcurrent concentration and minimum internal resistance, the amount ofanolyte between the anode and the diaphragm must be as thin as possiblein the form of a thin sheet or film, and that such a lm must becontinually circulated both for the purpose of carrying away from theimmediate anode sur- `face the high concentration of persulphuric acidas rapidly as formed, and also the heat, and further to reduce anytendency to polarization. In such a cell I ind it advantageous to coolboth the anolyte and catholyte, but do not nd it necessary to userefrigeration for this purpose in order to maintain the desired workingtemperature at the desired high current concentration employed. Previousattempts at this electrolysis required electrolyte temperatures of below10 C. 60

to 15 C.

The above advantages are all realized in an electrolytic cell whereinthe anolyte, diaphragm, catholyte and cathode are concentric, with theanode at the center because thereby its entire surface is effectivelyutilized and its volume is at a minimum. The anolyte is preferablycirculated lengthwise of the anode as a thin' sheet in a narrow annularspace between the anode and diaphragm. Inasmuch as platinum is today thepreferable anode material, the total cost .of platinum in a large plantbecomes very material,

but by having a platinum anode at the center within the anolyte, or in acentrally located concentric anode chamber, the total investment forplatinum is materially reduced. The lead cathode can conveniently be inthe form'of a coiled tube encircling the diaphragm, through whichcooling water can be passed to maintain the desired catholytetemperature. sistance of a cell constructed as above described issubstantially less than that of any prior cell with which I am familiar,and a current concentration can be employed from two to upwards of Theinternal reve times that heretofore employed in any cell g5 with which Iam familiar. I have been able by using current concentrations of between300 and 550 amperes per liter, and preferably about 400 to 450 amperesper liter to obtain exceptionally valuable results.

Previous attempts to produce per-sulphuric acid or persulphatesv in highconcentrations furthermore have not been successful since in all casesthe electrolysis was carried on -in a large volume of liquid in a singlevessel. This arrangement did not allow of rapid diffusion of thepersulphuric acid from the anodes and decomposition and overheatingresulted. I have overcome this by utilizing a small volume of liquid perunit of anode surface and by electrolyzing in this space with a highcurrent concentration. In order now to increase the total overallconcentration of persulphuric acid, a further feature of my inventioncomprises the operation in cascade I of a number of such cells.Operating in this way I have obtained solutions containing up to 30% ormore of per-sulphuric acid with high yields at a temperature of about 20C. These remarkable results have hitherto never been attained.

Inasmuch as a number of anodes and dia- 'or oval.

phragms as above described can be connected in parallel in onecatholyte, it is Within the broad scope of this invention to connectsingle cells in cascadeor a plurality of units having a single catholyteand multiple vanode units in cascade. Besides the advantage realized inincrease of overall concentration of per-sulphuric acid by cascading'ofcells, I have found that while the anolyte may be circulated from cellto cell, and

the catholyte similarly circulated from cell to l,- a decided gain inyield is obtained if the anolyte from the last unit, after being treatedto separate hydrogen peroxide, is then passed through the catholytecirculating system before being returned to the anolyte circulatingsystem. Apparently the cathodic action on this regenerated slphuric acidremoves substances which a cascade arrangement of cells for seriesoperation in a continuous process; Fig. IV shows in detail the method ofanode insertion inthe anode chamber; Fig.. V shows a slotted porous diskand Fig. VI shows one form of anode strip. The same numbers are usedthroughout to .designate the same or similar portions of each cell.

Referring to the drawings, 1 is the cell container, constructed ofmaterial resistant to the action of the electrolyte or lined with suchmaterial, such as lead or a resinuous compound. The container isprovided with an overflow 2, at or near the top. The container is shownas having a round cross section but may be square In the center of thecontainer is a cylindrical diaphragm 3 of thin porous material 'andclosed at the bottom; this may be of unglazed porcelain. The spacebetween the diaphragm and the container wall forms the cathode chamber.The cathode chamber is made large enough to carry a lead coil 14 whichserves as the cathode and also for carrying cooling water. An overflow 4is provided near the top of the diaphragm. cylinder above the containerwall. Inside the diaphragm cylinder is a glass'tube l5 open at the topbut sealed at the bottom having a glass tube 6 leading through the sealinto the anode chamber at 7. An overflow 13 leads from near the top ofthe tube 5 over the top of the diaphragm. The tube 5 is of such diameterthat a narrow annular space 8 of less than about 3 millimeters is formedbetween the tube and the diaphragm.v This narrow space is the anodechamber. The glass tube 5 rests on a slotted porous disk 21 (Fig. V).

The anode may be any suitable arrangement of non-attackable metal havingthe proper electrolytic characteristics, such as platinum, inserted inthe anode chamber 8. I prefer to construct my anode as follows:

A lead ring 9 having a connector 10` is fitted over the tube 5 and restson a shoulderll formed on the tube. On the circumference of the ring 9 Ifasten several strips 12 o1' platinum of such length that they reachwell into the anode chamber. The length of the strips and the number ofthe strips may be varied tu adjust the anode surface to any-amountdesired, The amid? Surcarried up and over the edge of the containeripa/,cai

face is adjusted so as to give an anode current density of less than 2amperes and preferably about 0.6.to 0.8 amperes per square centimeter. Ihave found that very thin platinum strips may be used; these arepreferably reenforced by being rivetted or clamped to a strip of othermetal not attacked during the electrolysis. Thus I have found that ananode strip of tantalum and platinum such as described in my U.S.P.1,477,- 099 one form of which is shown in Fig. VI, gives satisfactoryresults even though the tantalum is in contact with the electrolyte. Thestrips are fastened to the lead anode ring by rivets, screws, or bybrazing or soldering.

The cathode is formed by the coil of lead'tubing 14 arranged in thecathode chamber. A lead connector 15 is fastened to the coils to act asthe cathode lead. VThe lower end of the cathode coil is as at 16 andconnects with the cooling water supply 17 by a rubber or othernon-conducting tube 18. 'I'he upper end 19 of the cathode coil iscarried up and bent over so as to feed int`o a tube 20 inserted into theglass tube 5. Cooling of the anolyte can thus be effected. TheY coolingwater enters from 17 passes into the coil 14 and out at 19 into the tube20 to the bottom of 5 thence rising and overflowing through 13 to thesewer. The anolyte is cooled by contact with the outside of the glasstube 5. In some cases because of 155 structural features it ispreferable to cool the anolyte by a separate cooling water supply. Inthis case the cathode cooling water is run directly to the sewer and aseparate cold water supply led to the tube20 as shown in Fig. III.

In operation the anolyte is fed into the central tube 6 and flows to thebottom of the diaphragm cylinder and then rises in the anode chamber incontact with the anode and overows through 4. The catholyte is fed intothe cathode chamber and overflows through 2. The passage of the currentbetween the electrodes oxidizes the sulphuric acid or the sulphates toper-sulphuric acid or to the corresponding persulphate as the case maybe.

As noted above, the current concentration is a most important factor inthis electrolysis. It is now seen that I can easily apply high currentdensities per unit of volume. For example, if the anode chamber has anaverage diameter of about 5.0 centimeters, a depth about 50 cm. and athickness of 0.2-0.3 centimeter its vlume will be about 0.18 to .23liters. If 80 to 100 amperes are passed through there will be an anolytecurrent concentration lof between 300-550 amperes per liter.

'I'his type of cell construction enables meto obtain very low internaldiaphragm resstances. 'I'he diaphragm can be made very thin as it doesnot support weight nor is it exposed to unbalanced pressures. I can thusobtain voltage` drops of 135 less than 0.5 volts across a porous ceramicdiaphragm; the value of this is seen when itis realized that in previouswork on this problem diaphragm resistances have been such that voltagedrops of 0.8 to 1 volt have occurred'.

The rate of flow of the anolyte can of course vary within wide limits. Ihave found that a suitable rate in a cell of the above dimensions isabout 3.25 cc/ampere/minute. Thus if the 4cell is carrying a current of100 amperes the flow will 145. be about 0.325.1iters per minute. At'therates and current densities noted above and at about 20 C. I haveobtained a solution containing over 1% persulphuric acid from onepassage through the een. v'rms solution can be recirmuae in uner 15G ranode chamber of this cell to increase the persulphuric acid content;successive passages through such a cell will add to the per-sulphuricacid concentration until a concentration of well over 25% is reached.

In order to rapidly secure high concentrations of per-sulphuric acid insubstantial amounts the anolyte is preferably passed through the anodechambers of several cells at a rapid rate. Any suitable number of thesecells, for example 20, may be arranged in a cascade system andinterconnected as shown in Fig. III. The anolyte is fed into the tube 6of the topmost cell, passes through the anode chamber and overiiowsthrough 4 into the anode feed tube 6 of the next cell; the catholyte islikewise fed into the topmost cell and overows through 2 into thecathode chamber of the next cell. The voltage drop across each cell isfrom 4 to 8 volts. This allows a series electri-` cal connection of thecascade, giving for 20 cells a total voltage drop of about to 160 volts.

In order to best utilize the current supply sev-- eral of these seriescascades may be arranged in parallel electrically. In this last case itis convenient to have a number of anode units including the diaphragm inone large cathode chamber containing one large lead cathode coil. Theseseveral anode units are connected together and then connected to thecathode of the preceding cell thus giving a series-parallel electricalconnection. The anolytes from each anode unit in such an arrangement owfrom one anode unit into a corresponding anode unit in the next setwhile the catholyte ows from the one connnon cathode chamber to thenext.

When the anolyte leaves the lowest cell of such a cascade it contains ahigh concentration of persulphuric acid; the persulphuric acid is nowdecomposed to give hydrogen peroxide and sulphuric acid. The recoveredacid is then raised to the upper cell and preferably made the catholytesupply. After passing the last cathode chamber the acid is returned tothe upper cell and then added to the anolyte supply. This anolyte supplyis adjusted by fresh acid and pure water so that its specic gravity willbe preferably about 1.285 although other concentrations may be used.

The anode chambers of the cells ofthe dimensions given above in a bankof 20 would have a total volume of 3.6 to 4.6 liters. The electrolytewould then be subjected to anode action for a total period of about l0to 15 minutes.

I have thus electrolyzed in a 17-cell bank of cells, as described above,a solution of sulphuric acid containing about 500 grams sulphuric acidper liter at a temperature of 20 C. to 21 C. and an anolyte currentconcentration of 400 amperes per liter. The anode current density wasabout 0.8 amperes/cm2. A 30.8% solution of persulphuric acid wasobtained with a current efficiency of 71.5%.

Solutions of sulphates can also be employed. Thus, I have electrolyzed asolution containing 20% ammonium sulphate, 2% sulphuric acid and 'lt/2%K2SO4 at a temperature of 35 C. in the above apparatus. The per saltsvwere obtained by cooling outside of the apparatus and showed a currentefficiency of 74%. I have also obtained satisfactory results but lowercurrent efliciencies at as low as 300 amperes per liter.

The cell described above is most suitable for4 my process but I do notwish to be limited to its structure since the high currentconcentration, thin flowing sheets of electrolyte and other features maybe attained in other structures equiva- Ysaid glass cylinder lent tothat described. `Nor do I wish to be limited to the exact rates,temperature and compositions given. My invention, as will be seen fromthe above, is applicable to a great variety of. solutions, therefore, inthe appended claims wherein I refer to sulphuric acid solutions I meannot only an aqueous solution of sulphuric acid alone, but I also intendto include such solutions containing various addition agents,stabilizers, etc., from which per-sulphuric acidor persalts can beobtained by anodic action.

1. An anode for an electrolytic cell comprising an annular conductingring having `suspended from its circumference an anode member comprisingplatinum.

2. An anode for an electrolytic cell comprising an annular lead ringhaving suspended from its circumference anode members consisting of anupper tantalum portion and a lower platinum portion mechanically united.

3. An anode for an electrolytic cell comprising an annular lead ringhaving suspended from its circumference anode members consisting of atantalum portion and a platinum portion mechanically united.

4. An anode member for an electrolytic cell comprising a supportingtantalum member having a platinum member mechanically fastened to andsuspended from it.

5. An anode chamber unit for electrolytic cells comprising a cylindricalporous diaphragm having glass cylinder inserted therein'so as to form anarrow annular anode chamber between said glass wall and said diaphragm.A

6. An anode chamber unit for electrolytic cells comprising a cylindricalporous f diaphragm having glass cylinder inserted therein so`as to forma narrow annular anode glass wall and said diaphragm of less than 0.3L

chamber betweenl said` vided-with an overflow and closed at the bottom,i

a glass cylinder sealed at theA bottom and lprovided with an overflowinserted in said porous cylinder so as to form a narrow annular anodechamber between said glass cylinder land said diaphragm and a glasstubey inside said glass cylinder and leading through said sealed bottomand communicating with said anode chamber.

8. In an apparatusv for the electrolytic productionof persulphuric acida centrally located annular anode chamber having a depth between anodeand diaphragm of less than 0.3 centimeters.

9. A cell for the electrolytic production of persulfuric acid comprisinga centrally located anode assembly consisting of an anode member in anarrow anode chamber, said chamber being formed by an imperviouscylinder and a porous diaphragm concentric therewith, and a concentriccathode chamber about said diaphragm.

l0. An electrolyticcell comprising a container, a coiled lead tubecathode, a cylindrical closedbottom porous diaphragm provided with anoverflow inside the coils of said cathode, a glass cylinder sealed atthe bottom, and provided with an overflow, inserted in saidporouscylinder so as toform a narrow annular anode chamberbetween andsaid diaphragm, a glass tube inside said glass cylinder leading throughsaid sealed bottom so as to communicate with said anode chamber and ananode suspended in said anode chamber.

11. An electrolysis system comprising a plurality of cells according toclaim 9 in cascade flow arrangement and in series electrical connection,means connecting the anolyte overow of each cell but the lowest with theanolyte supply tube of the next lower cell, means connecting thecatholyte overllow of each cell but the lowest with the cathode chamberof the next lower cell,

means for separately supplying anolyte and.

catholyte to the upmost cell and means for separately collecting saidanolyte and catholyte owing from the lowest cell. 12. An electrolysissystem for the production of per salts comprising a plurality of cells,having anode and cathode chambers,in cascade ow aring from the lowestcell.

GUSTAV BAUM.

